The present invention relates to apparatus for conditioning tobacco, and more particularly to improvements in apparatus for reducing the moisture content of tobacco. Still more particularly, the invention relates to improvements in apparatus wherein tobacco is dried during travel through a conditioning zone wherein the particles of tobacco are brought into indirect and/or direct contact with a heating fluid.
In certain presently known dryers, the moisture content of tobacco is reduced during travel through a rotating drum which is heated by one or more coils. As a rule, steam which is circulated in the coils provides a basic or primary heating action which may but need not be adjustable. The coils come into direct contact with tobacco particles and/or heat the rotating drum. In most instances, fresh steam is admitted into and spent steam is evacuated from the coils at the outlet or discharge end of the drum.
It is also known to reduce the moisture content of tobacco by admitting a hot gaseous fluid (e.g., air) at the inlet or at the outlet of the rotating drum, i.e., hot air can flow concurrent with or countercurrent to the direction of tobacco travel through the conditioning zone. Certain presently known dryers are provided with means for admitting a hot gaseous fluid concurrent as well as countercurrent to the direction of tobacco travel, for example, in such a way that the upstream half of the conditioning zone receives hot air which flows toward the outlet and the downstream half of the conditioning zone receives hot air which flows toward the inlet of the drum. Spent air is evacuated from the median portion of the conditioning zone, i.e., substantially midway between the ends of the drum.
Each of the just enumerated conventional apparatus exhibits important advantages as well as one or more serious drawbacks. Thus, dryers which are designed exclusively for concurrent flow of hot gases can utilize relatively simple and inexpensive controls which insure that the final moisture content equals or approximates an optimum value. The controls of a dryer for countercurrent flow of hot gases are much more complex and expensive. However, a dryer for countercurrent flow of hot gases exhibits the advantage that tobacco particles which are about to leave the conditioning zone are contacted by very hot gases. This enables the hot gases to influence casing and other flavoring agents so that the additives effect more pronounced and highly desirable changes in taste and/or other qualities of tobacco. The dryers wherein the drum receives hot gases at both ends must be equipped with expensive and highly complicated controls, and the evacuation of spent gases midway between the ends of the drum also presents many problems, mainly because the drum rotates.